Optical unit and LCD device using the optical unit

ABSTRACT

An optical unit comprises a frame. A light conductive plate is combined with the frame only and stationary relative thereto.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical unit for use in aliquid crystal display (LCD) device, and to a LCD device incorporatingsuch optical unit.

[0003] 2. Description of the Related Art

[0004] In the field concerning miniaturized LCD devises, use of anoptical unit as a built-in backlight has widely spread. Commonly, suchoptical unit includes a light conductive plate and a source of light,for example, a fluorescent tube or LED. The incident light from thesource of light impinges upon the adjacent edge of the light conduciveplate. The light diffuses within the light conductive plate. Thediffused light illuminates the associated LCD through a planar surfaceof the light conductive plate. A light reflective sheet covers at leasta portion of the light conductive plate to reflect the diffused lightback inwardly. This so-called edge type system is advantageous inthinness.

[0005] One example of the edge type system is illustrated in FIGS. 11and 12. FIG. 11 is a plan view of an optical unit 120 according to theprior art with unnecessary sheets removed to illustrate a frame 102.FIG. 12 is a cross section taken through the line 12-12 in FIG. 11. Theframe 102 is a rectangular receptacle with a shallow rectangular space.The frame 102 includes four-sided inner peripheral wall and an end wall,which are interconnected to define the shallow rectangular space. Asbest seen in FIG. 12, the frame 102 receives within the shallowrectangular space a reflective sheet 103 covering the end wall, a lightconductive plate 101, and a LED 113. The frame 102 has two positioninggrooves 112, with which the opposed sides of the inner peripheral wallare formed, respectively. The light conductive plate 101 has twopositioning projections 111 inserted into the positioning grooves 112,respectively. The two projections 111 extend outwardly from sides of thelight conductive plate 101. The light conductive plate 101 has a surfacecovered with a lens sheet 104 and a diffusion sheet 105. The lens sheet104 extends over almost the entire area of the surface of the lightconductive plate 101. The diffusion sheet 105 covers the entire area ofthe surface of the lens sheet 104. An antiglare sheet 107, which isformed with a rectangular opening, is fast on the frame 102 by adhesive106 in a manner to cross the boundary between the inner peripheral wallof the frame 102 and the light conductive plate 101 (see FIG. 12).

[0006] The market of mobile terminals are growing bigger and bigger.Personal digital assistants (PDA) and mobile telephones constitute themarket. In the market, there is strong demand for a reduction inthickness, weight and cost of LCD devices for beneficial application tothe PDA and mobile telephones. Accordingly, a need remains for a thin,light and inexpensive optical unit.

[0007] The illustrated known optical unit 120 does not meet this need toa satisfactory level. In this known unit, the end wall of the frame 102plays an important role in retaining an appropriate relationship betweenthe light conductive plate 101 and light reflective plate 103.

[0008] With regard to the relationship between a light conductive plateand a frame, JP-A 11-305228 proposes interposing a light conducive platebetween a frame and a light reflective sheet and adhering the lightreflective plate to the frame. Without the light reflective plate, thelight conductive plate would drop out of the frame because it is notheld stationary relative to the frame. The light conductive plate isfast on the frame by adhesive only. Thus, there is potential problemthat the appropriate positional relationship between the lightconductive plate and the frame may not hold if the light conductiveplate is stressed against the light reflective sheet.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a thin opticalunit, in which a light conductive plate is reliably held in theappropriate positional relationship with the associated element(s).

[0010] Another object of the present invention is to provide a LCDdevice incorporating an optical unit of the above kind.

[0011] According to one exemplary implementation of the invention, thereis provided an optical unit comprising:

[0012] a frame; and

[0013] a light conductive plate combined with the frame only to bestationary relative thereto.

[0014] According to another exemplary implementation of the presentinvention, there is provided an optical unit for a liquid crystaldisplay device, comprising:

[0015] a light conductive plate;

[0016] a source of light arranged to impinge light to an edge of thelight conductive plate; and

[0017] a retainer, including a light reflective sheet portion, keepingthe light conductive plate, the source of light and the light reflectivesheet portion in an appropriate positional relationship.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be apparent from the following moreparticular description of exemplary embodiments of the invention asillustrated in the accompanying drawings. The drawings are notnecessarily scale, emphasis instead being placed upon illustrating theprinciples of the invention.

[0019]FIG. 1 is a plan view of one exemplary implementation of anoptical unit according to the present invention, with unnecessaryelements removed to illustrate a frame and a light conductive platecombined with the frame only to be stationary relative thereto.

[0020]FIG. 2 is a cross section taken through the line 2-2 in FIG. 1.

[0021]FIG. 3 is a similar to FIG. 1, illustrating a modification of theexemplary implementation.

[0022]FIG. 4 is a cross section taken through the line 4-4 in FIG. 3.

[0023]FIG. 5 is a plan view of another exemplary implementation of anoptical unit according to the present invention, with unnecessaryelements removed to illustrate a frame and a light conductive platecombined with the frame only to be stationary relative thereto.

[0024]FIG. 6 is a cross section taken through the line 6-6 in FIG. 5.

[0025]FIG. 7 is a plan view of another exemplary implementation of anoptical unit according to the present invention.

[0026]FIG. 8 is a cross section taken through the line 8-8 in FIG. 7.

[0027]FIG. 9 is a cross section taken through the line 9-9 in FIG. 7.

[0028]FIG. 10 is an unfolded view of a retainer including a lightreflective portion.

[0029]FIG. 11 is a plan view, similar to FIG. 1, of the before discussedoptical unit according to the prior art.

[0030]FIG. 12 is a cross section taken through the line 12-12 in FIG.11.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0031] Referring to the accompanying drawings, like reference numeralsare used to designate like parts or portions throughout each view ofFIGS. 1 to 10 for the sake of brevity of description.

[0032]FIGS. 1 and 2 illustrate one exemplary implementation an opticalunit 20 of the present invention. The optical unit 20 includes a lightconductive plate 1 and a frame 2. The light conductive plate 2 isrectangular and has four sides. Molding has formed the frame 2. Theframe 2 has a rectangular opening and includes four-sided innerperipheral wall defining the rectangular opening.

[0033] The light conductive plate 1 is combined with the frame 2 only tobe stationary relative to it. In the illustrated optical unit 20, thelight conductive plate 1 is held stationary, within the rectangularopening, relative to the frame 2. The light conductive plate 1 has fourfixing projections 8, which are inserted into and received by fourfixing hollows 9, respectively. The frame 2 is formed with the hollows9. The four fixing hollows 9 are located in two opposed sides of theinner peripheral wall of the frame 2, two in one of the two opposedsides, the other two in the other side. The four fixing projections 8are located in two opposite sides of the light conductive plate 1, twoin one of the two opposite sides, the other two in the other side. Withthe fixing hollows 9 receiving the fixing projections 8, the frame 2retains the light conductive plate 1.

[0034] On one of the four sides, the light conductive plate 1 has alight receiving edge positioned near a translucent tube 10. The lightconductive plate 1 has a front surface and a rear surface. A lightreflective sheet 3 covers the entire area of the rear surface of thelight conductive plate 1. At portion near the periphery, the lightreflective sheet 3 is fast on one end surface of the frame 2 by adhesive6, for example, a pressure sensitive adhesive double-coated tape.Optical sheets cover the front surface of the light conductive plate. Inthe illustrated optical unit 20, a lens sheet 4 covers the entire areaof the front surface of the light conductive plate 1, and a diffusionsheet 5 covers the entire area of the surface of the lens sheet 4. Anantiglare sheet 7, which is formed with a rectangular opening defining alight discharge region, is fast on the opposite end surface of the frame2 by adhesive 6 in a manner to cross the boundary between the innerperipheral wall of the frame 2 and the light conductive plate 1. Theantiglare sheet 7 keeps the diffusion sheet 5 and lens sheet 4 inappropriate position on the surface of the light conductive plate 1.

[0035] From the preceding description on the optical unit 20, it isappreciated that the frame 2 does not require a bottom end wall andretains the light conductive plate 1 by holding the sides of it.Employing the frame 2 without the bottom end wall makes greatcontribution to a reduction in thickness of the optical unit 20. Areduction in thickness as much as 20% has resulted from comparison ofthe optical unit 20 with the known optical unit 120.

[0036] In addition to coupling between the light conductive plate 1 andthe frame 2, the antiglare sheet 7 and the light reflective sheet 3interpose therebetween the light conductive plate 1 to hold the lightconductive plate 1 firmly within the frame 2. This causes an increase instiffness of the optical unit 20. In other words, the frame 2, lightreflective sheet 3 and antiglare sheet 7 cooperate with each other toform a retainer, which can keep the light conductive plate 1 and theassociated optical sheets 4 and 5 in the appropriate positionalrelationship even under external stress. This brings about a reductionin damage on the light conductive plate 1, enhancing reliability of theoptical unit 20.

[0037] The number of fixing projections 8 and hollows 9 is not limitedto four (4). The number may be any appropriate even number that isdetermined after due consideration of design requirement on therelationship between the light conductive plate 1 and frame 2. Forexample, the number may be two (2) or six (6).

[0038] In the optical unit 20, the light conductive plate 1 has thefixing projections 8, and the frame 2 has the fixing hollows 9. Thepresent invention is not limited to this example. The fixing projectionsmay belong to the frame, and the fixing hollows to the light conductiveplate.

[0039]FIGS. 3 and 4 illustrate a modification. A modified optical unitis generally indicated at 20A. The optical unit 20A is substantially thesame as the previously described optical unit 20. However, the opticalunit 20A is different from the optical unit 20 in the provision ofpositioning projections 11 and positioning grooves 12. A frame 2 hasfour positioning grooves 12, two on one of two opposed sides of theinner peripheral wall, the other two on the other side. These twoopposed sides are free from the fixing hollows 9. A light conductiveplate 1 has four positioning projections 11 inserted into and receivedby the positioning grooves 12, respectively. The two of the fourpositioning projections 11 extend outwardly from one of two oppositesides, and the other two positioning projections 11 from the other side.These opposite sides are free from the fixing projections 8. Anotherdifference resides in the use of LED 13 as a source of light instead ofthe fluorescent tube 10.

[0040] In the modified optical unit 20A, the positioning work of thelight conductive plate 1 becomes easy due to the provision of thepositioning projections 11 and grooves 12.

[0041]FIGS. 5 and 6 illustrate another exemplary implementation of anoptical unit 40 according to the present invention. The optical unit 40is substantially the same as the optical unit 20. However, the opticalunit 40 is different from the optical unit 20 in that the antiglaresheet 7 has been eliminated. The optical unit 40 has eliminated theantiglare sheet 7 by using a slightly enlarged diffusion sheet 15. Asbest seen in FIG. 6, the diffusion sheet 15 covers also the end surfaceof a frame 2. At an area portion immediately inward of the periphery,the diffusion sheet 15 is fast on the end surface of the frame 2 byadhesive 6.

[0042] Elimination of the antiglare sheet 7 has provided a furtherreduction in thickness in the optical unit 40 as compared to thepreviously discussed optical unit 20.

[0043] FIGS. 7 to 10 illustrate another exemplary implementation of anoptical unit 60 according to the present invention.

[0044] Before entering the description on the optical unit 60, it is tobe remembered that, in the optical unit 20 illustrated in FIGS. 1 and 2,the frame 2, light reflective sheet 3 and antiglare sheet 7 cooperatewith each other to form a retainer, which can keep the light conductiveplate 1 and the associated optical sheets 4 and 5 in the appropriatepositional relationship.

[0045] The optical unit 60 is substantially the same as the optical unit20 in that the retainer keeps the light conductive plate 1 and theassociated optical sheets 4 and 5 in the appropriate positionalrelationship. However, as different from the optical unit 20, a retainer3A of the optical unit 60 is a single piece made of a light reflectivesheet. Accordingly, the optical unit 60 does not use the frame 2 and theantiglare sheet 7, which are used in the optical unit 20 as constituentelements of the retainer.

[0046] With reference to FIG. 10, the illustrated shadowed areas 35indicate one area portion where the retainer 3A is fast on the rearsurface of the light conductive plate 1 (see FIGS. 8 and 9) by adhesive6 and another area portion where the retainer 3A is fast on the surfaceof the diffusion sheet 5 on the lens sheet 4. The retainer 3A includesan integral rectangular light reflective sheet portion surrounded by theabove-mentioned one area portion 35. This rectangular light reflectivesheet portion cover the rear surface of the light conductive plate 1when the retainer 3A is folded and fast on the light conductive plate 1and the diffusion sheet 5. The retainer 3A is formed with a rectangularopening 34 that is surrounded by the above-mentioned another areaportion. This rectangular opening 34 defines a light discharge region onthe diffusion sheet 5 over the front surface of the light conductiveplate 1.

[0047] The following explanation on the manner of assembly may help thereader to understand the advantageous feature of the optical unit 60.

[0048] First, attach a fluorescent tube 30 via flexile cable 22 to thelight conductive plate 1 near the light receiving edge.

[0049] Second, lay the lens sheet 4 over the front surface of the lightconductive plate 1.

[0050] Third, lay the diffusion sheet 5 over the surface of the lenssheet 4.

[0051] Fourth, with the rectangular light reflective sheet portion laidover the rear surface of the light conductive plate 1, fold the retainer3A in a manner to wrap the light conductive plate 1, fluorescent tube 30and diffusion sheet 5.

[0052] Fifth, press the retainer 3A along the area portions 35 to fastit on the rear surface of the light conductive plate 1 and on thediffusion sheet 5 via adhesive 6 as shown in FIGS. 8 and 9.

[0053] From the preceding description, it is appreciated that theoptical unit 60 is advantageous over the optical unit 20 in a reductionof the number of constituent components because the frame 2 is no longerneeded.

[0054] The optical units 20, 20A, 40 and 60 can be incorporated as abacklight in the usual manner as a component of LCD devices toilluminate LCD.

[0055] In one embodiment, a liquid crystal display device comprises aliquid crystal, a pair of substrates having interposed therebetween theliquid crystal, and an optical unit 20 or 20A or 40 or 60 arranged onone side of one of the pair of substrates.

[0056] While the present invention has been particularly described, inconjunction with exemplary implementations, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

[0057] This application claims the priority of Japanese PatentApplication No. 2002-057275, filed Mar. 4, 2002, the disclosure of whichis hereby incorporated by reference in its entirety.

What is claimed is:
 1. An optical unit comprising: a frame; and a lightconductive plate combined with the frame only to be stationary relativethereto.
 2. The optical unit as claimed in claim 1, wherein the lightconductive plate is fixed to the frame by inserting fixing projectionsinto fixing hollows, respectively.
 3. The optical unit as claimed inclaim 2, wherein the frame has an opening receiving the light conductiveplate, and an inner peripheral wall defining the opening, and whereinthe fixing hollows are located in the opposed sides of the innerperipheral wall.
 4. The optical unit as claimed in claim 3, wherein anantiglare sheet is fast on one end surface of the frame in a manner tocross the boundary between the frame and one surface of the lightconductive plate.
 5. The optical unit as claimed in claim 3, wherein adiffusion sheet is fast on one end surface of the frame in a manner tocover the frame and one surface of the light conductive plate.
 6. Theoptical unit as claimed in claim 4, wherein a light reflective sheet isfast on the opposite end surface of the frame in a manner to cover theframe and the opposite surface of the light conductive plate.
 7. Theoptical unit as claimed in claim 5, wherein a light reflective sheet isfast on the opposite end surface of the frame in a manner to cover theframe and the opposite surface of the light conductive plate.
 8. Anoptical unit comprises: a light conductive plate; a light reflectivesheet; and at least one optical sheet on one surface of the lightconductive plate, which is one of optical sheets that include adiffusion sheet and a lens sheet, wherein the light reflective sheetextends to partially cover the optical sheet and the light conductiveplate except a light discharge region on the one surface of the lightconductive plate, and the reflective sheet is fast on the lightconductive plate at an area portion near the periphery of the lightconductive plate.
 9. A liquid crystal display device comprising: aliquid crystal; a pair of substrates having interposed therebetween theliquid crystal; and an optical unit arranged on one side of one of thepair of substrates, the optical unit including a frame and a lightconductive plate combined with the frame only to be stationary relativethereto.
 10. A liquid crystal display device comprising: a liquidcrystal; a pair of substrates having interposed therebetween the liquidcrystal; and an optical unit arranged on one side of one of the pair ofsubstrates, the optical unit including; a light conductive plate; alight reflective sheet; and at least one optical sheet on one surface ofthe light conductive plate, which is one of optical sheets that includea diffusion sheet and a lens sheet, wherein the light reflective sheetextends to partially cover the optical sheet and the light conductiveplate except a light discharge region on the one surface of the lightconductive plate, and the reflective sheet is fast on the lightconductive plate at an area portion near the periphery of the lightconductive plate.
 11. A liquid crystal display device incorporating theoptical unit as claimed in claim
 1. 12. A liquid crystal display deviceincorporating the optical unit as claimed in claim
 8. 13. An opticalunit for a liquid crystal display device, comprising: a light conductiveplate; a source of light arranged to impinge light to an edge of thelight conductive plate; and a retainer, including a light reflectivesheet portion, keeping the light conductive plate, the source of lightand the light reflective sheet portion in an appropriate positionalrelationship.
 14. The optical unit as claimed in claim 13, wherein theretainer includes a frame with an opening receiving the light conductiveplate, and an antiglare sheet fast on one end surface of the frame, thelight reflective sheet portion is a light reflective sheet fast on theopposite end surface of the frame.
 15. The optical unit as claimed inclaim 13, wherein the retainer is a single light reflective sheetincluding the light reflective sheet portion.